Method of producing composite semicrystalline articles



Jun 13, 1967 ca. E. s-rows 3,325,266

METHOD OF PRODUCING COMPOSITE SEMICRYSTALLINE ARTICLES Filed April 14, 1.966

INVENTOR. 60v 1.. drama- ATTORNEY United States Patent M 3,325,266 METHOD OF PRODUCHNG COMPOSHTE SEMICRYSTALLINE ARTICLES Guy E. Stong, Elmira, N.Y., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed Apr. 14, 1966, Ser. No. 549,100 3 Claims. (Cl. 65--33) This application is a continuation-in-part of my pending application, Ser. No. 324,165, filed Nov. 12, 1963, now abandoned which application was in turn a continuation-in-part of Ser. No. 19,650, filed Apr. 4, 1960, and now abandoned.

This invention relates to a method of making composite crystalline bodies by joining together individual elements thereof into a single unitary structure. Semicrystalline bodies are made by the controlled crystallization by heat treatment of a glass body according to the method disclosed in Patent No. 2,920,971, and have the same physical structure as the articles described in that patent. Wherever the term semicrystalline materials (body, element, etc.) is used throughout the present specification and claims it shall be understood to mean a material so produced. As is pointed out in such patent, one of the primary advantages of such a method is that articles can be produced from the molten glass body by conventional glassforming techniques such as pressing, blowing, drawing and the like and thereafter can be transformed into a semicrystalline body, having the desirable properties thereof, by heat treating the preformed article without substantially changing its size and shape. Although such articles have some characteristics, such as zero porosity and high strength, which make them more desirable than conventionalceramic bodies produced by sintering ceramic batches, fabrication of complex bodies therefrom have presented many problems.

First of all, the shapes which can be formed from the molten glass are somewhat limited. Secondly, preformed elements of such glasses can be joined only with ditficulty by conventional glass techniques such as lamp-working because reheating of portions of the glass tends to produce crystallization, thereby introducing areas of weakness in .the body during such operation or upon the subsequent heat treatment to produce controlled crystallization throughout the entire structure. While elements which have been heat treated to cause the controlled crystallization thereof can be joined together into complex structures by known ceramic methods such as metallization and soldering or with metallic coupling devices, these methods are not altogether suitable, especially for applications wherein the product is subjected to elevated temperatures or to sudden and/or repeated changes in temperature.

The primary object of this invention is to provide a method for making composite, unitary semicrystalline ceramic bodies.

Another object is to provide a method for producing a composite semicrystalline body which can withstand thermal cycling.

A still further object is to provide a method for producing a composite semicrystalline body which can withstand elevated temperatures.

The accompanying drawing illustrates a novel optical mirror produced by the method of this invention.

The method of this invention broadly comprises the application to selected areas of at least one preformed element of the desired structure a cementing composition consisting essentially of at least one fluoride salt selected from the group consisting of LiF, NaF, KF, MgF CaF SrF BaF PbF and ZnF placing the thus coated surface in contacting relationship with another preformed 3,325,266 Patented June 13, 1967 element, and thereafter heating the bodies to a tempera ture of at least 800 C.

While it is not possible to find the reasons why thi: process produces such satisfactory bonds between tilt semicrystalline ceramic elements, it is believed that wher the cementing composition is heated, it produces flui products either by melting or reaction with the semi crystalline material, which readily wet the surface of th bodies to be joined and also permeate each of such surface: to form a bridging structure extending beneath the sur faces of each of the bodies and that the mlCIOSCOPlt crystals present in the semicrystalline bodies cause an: reaction product formed by the action of the cementing composition on the semicrystalline body to crystallize tr a desirably fine-grained structure. Because such reactior apparently does occur and is necessary in order to pro vide a satisfactory bond, attempts to join stable glasse. by such a method result in coarse-grained devitrificatior and checks occurring in the glass, whereas attempts tr join conventional sintered-ceramic bodies in a simila fashion results in fused zones :at the interface whicl readily crack upon cooling.

More specifically, the objects of my invention an achieved by first producing elements of the desired struc .ture in a conventional manner from the molten glass a described in the above-mentioned patent. The element may then be further conformed to the desired configura tion by such mechanical finishing means as grinding an cutting, or the elements may be converted to the semi crystalline condition by heat treatment thereof accordin to the aforementioned patent prior to such finishing oper ations inasmuch as my method can be utilized to job elements which have been converted to the semicrystallinr condition, or to join elements simultaneously with thi heat treatment which produces the semicrystalline bod from the glass.

A cementing composition consisting essentially of a least one of the above enumerated fluoride salts is there upon applied to the selected areas of the thus formed ele ments. The cementing composition can be applied in an convenient manner such as by dissolving the salts in th solvent and thereafter spraying or brushing the solutioi on the desired areas or by dipping the desired areas intr the solution. Furthermore, it is also possible to prepar a suspension or paste of the cementing composition whici can be brushed or spread on the desired surfaces. Th solvent or the carrier liquid can thereafter readily be re moved by evaporation from the surfaces to leave the es menting composition thereon. A particularly suitabl method for applying the cementing composition comprise suspending the cementing composition in an organic film forming solution such as cellulose acetate and the like and thereafter evaporating the solvents from such organi material to produce a film of uniform thickness contain ing the cementing composition suspended evenly through out. Thereafter it is possible to cut from such film portion having the desired shape and placing them upon th surfaces to be joined. The subsequent heating step there after eliminates the organic material from the film an deposits the cementing composition upon the desired area of the bodies.

The elements are joined by placing the elements i contacting relationship with the film or layer of cementin composition sandwiched therebetween, and placing ther in a furnace, the elements being maintained in thei correct relationship by suitable supporting means suc as a jig or clamps. The furnace is them heated to a ten perature of at least 800" C. and preferably in excess c the melting point of the cementing composition but belo the point at which the cementing composition boils c decomposes and also below the deformation temperatur f the elements, i.e. the temperature at which the elements TABLE H eform and thereby lose their desired shape. While the me necessary for a good joint to be achieved by thls Example No. cementing Composition M.O.R. (p.s.i.)

iethod varies with the temperature, the minimum temeratures requiring the longest time, I have found that NaF 1,600

1e preferred method comprises maintaining a tempera- F 228 ire of about 1100 C. to 1400 C. for a time of about 1:300 to 8 hours. However, some of the advantages of this @5 2 1,450 iethod can be achieved with a time as short as /2 hour 3 1 1:800 ven at a temperature of about 800 C. Of course, when 1- racticing the particular embodiment of this invention 'hich comprises joining elements simultaneously with 1e heat treatment utilized to controllably crystallize the lass to the desired semicrystalline condition, the heat 'eatment utilized must be that which is dictated in order Cross bars of glass having the ccfmposltlon fl l produce th d i d crystallization B in Table I were assembled as descr1bed above utlhzlng Examples 9-23 Table I sets forth the compositions of seven glasses the cementiflg Compositions setfollh in Tab1$ III and hich are representative of the wide variety of materials 0116 Serles 0f P slmultaneously lomed f hich can be utilized in the above-described process. Convfirted t0 samlcfystallllle Ceramlc bodles y heatlng )ther glass compositions operable in my invention are reat P Ininutfi t0 d at fQf 1 hour, orded in Patent No. 2,920,971 which has been referred heated to 1150 at P minute, held at 1150 3 above and these are incorporated by reference herein. f0? 4 hours and thereafter cooled to room temperature at 4 C. per minute. The composite semicrystalline bodies thus formed were tested as described above and the TABLE I modulus of rupture, set forth in Table III, determined.

A B 0 D E F G TABLE III Example No. cementing Composition M.O.R. (p.s.i.)

LiF 3, 200 N21]? 2, 200 KF 1, 400 car; 1, 100 sm 1, 400 PbFz 1, (s00 Another series of such samples was simultaneously joined and converted to semicrystalline ceramic bodies by heating at 5 C. per minute to 800 C., held at 800 C.

To demonstrate the effectiveness of my present process, for 1 hour, heated to 1000 at P Inlnute, he1d at prepared sample bars of each of the above compositions, 10000 C for 2 hours, heated to 11900 at 19 ome of which had been crystallized to the semicrystalline me, held at 1190 C- f r 4 h urs, and cooled to room temondition by heat treatment thereof, of a size of about Reramrefit P hour- The composlte P y 2 inch square b 1 inch10ng Th Samples were ground line bodies thus formed were tested asdescrrbed above 11 a conventional grinder to produce flat surfaces thereand F modulus of rupture, Set forth In Table V, n. Suitable cementing compositions were then prepared termlned' 1 a paste form by mixing with a small amount of butyl TABLE IV lcohol and the cementing composition was spread on the riddle of a /2" x 1" surface of one test bar for a E' l'N. o t C t M... istance of /2 A second simllar test bar was then placed 0 0 men mg mp0s] O R (p 51) n the cementing composition at right angles to the axial 2 S00 :ngth of the first test bar, thus giving an area of contact 11700 etween the two bars of A1 inch square. The butyl alcohol 288 as then allowed to evaporate from the film and the .percontNaF est bars fired to produce the desired bond. After firing, W percent L1F 1 4 so no strength of the bond was determlned by measuring .pereent N :1F J Y 0 1e force, applied in the direction perpendicular to the 'percentLlF-m 3 200 percent NaF rea of contact between the two bars, necessary to break .percent LiF 1e bond 1 percent NnF. 31200 23 Wt. percent; LiF 3 2 0 The examples hereinafter set forth show the strength [40 wt. perccntNaF 0 btainable for a wide variety of cementing compositions tilizing my novel method for producing composite semirystalline articles having the illustrative compositions Examples 25 -31 et forth in Table I.

Cross bars of semicrystalline material having the composition C in Table I were assembled as described above Cross bars of semicrystalline material of composition A utilizing the cementing compositions recorded in Table Iere assembled as described above utilizing the ce- V. The cross bars of the examples were joined by heating aenting compositions set forth in Table II, fired by heatat 5 C./minute to 1400 C., maintaining the temperaag to 1260 C. at 5 C. per minute, held at 1260 C. for ture thereat for 8 hours, and then cooling to room tem- Examples 1-8 hours, and cooled to room temperature at 3 C. per perature at 5 C./minute. The composite semicrystalline rimute. The composite semicrystalline bodies thus formed bodies thus formed were tested in the manner described Iere tested as described above and the modulus of rupabove and the modulus of rupture determined thereby ure, set forth in Table II, determined. is also recorded in Table V.

' TABLE VIII Examples 32-54 .2.C.ross bars of semicrystalline material having the composition D were assembled as described above wherein the cementing compositions set forth in Table VI were employed. The heating schedule utilized in the cement- Example No. Cemcnting Composition 78.7% Z11Fg+21.3% NaF (by wt.) 2, 78.7% ZnF +21.3% NaF (by wt.) 2, 65% CuFz+35% NaF (by wt.) 1,

Examples 44-45 Cross bars of semicrystalline material of compositio G were joined together in the manner described abov utilizing the cementing compositions set out in Table I) fired by heating to 815 C. at the rate of 5 C. per mir ute, maintained thereat for 8 hours, and thereafter coole to room temperature at 3 C. per minute. The sem crystalline bodies thus joined together into a unitary StllK ture were tested for mechanical strength and the modulu of rupture determined as described above.

ing operation was the same as that described above with respect; to the examples of composition C. The modulus TABLE IX of rupture measurements conducted on these examples are recorded in TableVI. Example N0. Cementing Composition I M.O.

(psi. TABLE VI g 44.-. 06.3% MgFg+33.7% ME (by wt.) 1, 0( Example No. Cementing Composition M.0.R. (psi) 45 78'7% ZHF2+2L3% NBF (by u 3L L300 A t' 1 1 't bl h d r 1 h 1,200 par rcu ary .8111 a e met 0 or app ymg t e ce L100 menting compos1t1on to the elements to be oined com PememMgF" prises utilizing an organic film containing the cementin Examples 35-39 Cross bars of semicrystalline material having the composition E were then assembled in accordance with the above-described method utilizing the cementing compositions recorded in Table VII. The heating schedule followed to yield a strong seal was identical with that set forth above with respect to the examples of compositions C and D. Table VII also includes the results of modulus of rupture measurements made on the examples.

TABLE VII Example No. Cemcnting Composition M.O.R. (p.s.i.)

35 NaF 1, 100 ltggFg i 1, 200 5 wt. percent Mg "2.. {53 wt. percent 1133211? l 800 5 wt. percent a z. 50 wt. percent BaFz 000 Lil 1, 000

Example Examples 41 43 Cross bars of semicrystalline material having the composition F were assembled as described above employing the cementing compositions recorded in Table VIII, fired by heating to 1200 C. at 100 C. per hour, held at 1200 C. for 8 hours, and then cooled to room temperature at 5 C. per minute. The composite semicrystalline articles thus fabricated were tested as described above and the modulus of rupture values set out in Table VIII obtained.

composition suspended therein. A preferred method 0 producing such a film comprises mixing the fluoride ce menting composition with about twice its weight of methyl methacrylate resin solution to obtain a uniforr mixture. A polymerization catalyst, benzoyl peroxide, i added to the mixture in an amount equal to about 1% of the weight of the resin. The mixture is poured out 01 a suitable surface, such as a glass plate coated with film of silicone parting material, and spread to a uniform film thickness. The film is allowed to cure and in so doin it shrinks to about half its original thickness. Thus a filn originally formed to a thickness of .007" cures to a thick ness of .004" and contains .08 gram of cementing com position per square inch of film. The film may be easil out with a knife or scissors to any desired shape an applied to the surface or surfaces to be joined.

The method has been found to be particularly suitabl for the manufacture of optical mirrors which will be mor fully described with reference to the drawing. The draw ing shows an isometric view of an optical mirror 10 com prising two flat, parallel discs 11 and 12 spaced apar from each other but joined into a unitary structure by multitude of cylindrical elements, such as 13; the bondin, of such elements being achieved by joint 14. As can b seen from the drawing, the cylindrical elements are ar ranged in symmetrical arrangement about the center 0 discs 11 and 12. The number of such elements will b determined by the size of the mirror and the size of th cylindrical elements; 37 tubes with an outside diamete of about 1' being suitably arranged in three concentri circles about a tube at the center of the discs for a mirro about 10" in diameter.

For such a mirror, glass elements having compositio: B are prepared to the desired size. The discs 11 and 11 are ground to 10 in diameter by A" thick and the tube with an OD. of about 1" and an ID. of about /8" ar ground to a length of 1". The ends of each tube are the: coated with the cementing composition utilized in Ex ample 19 and the elements are assembled in the desire relationship. The assembled article is then heated ac cording to the schedule utilized for Example 19 to con vert the glass to a semicrystalline body and join it into single unitary structure. The outer surface of the disc 1 is then ground to the desired optical surface.

A mirror formed by the above-described process was an tested by immersing one-half of it in a liquid mainned at 78 C. while the other one-half was mainned at about 20 C. No damage to the body or joints [8 observed. Furthermore, the mirror was subjected to shocks of Gs a total of times along each of three mutually rpendicular axes without damage to the joints. Since this invention has been demonstrated with the exiples set out in Table I, the compositions of which are dely varying, and the examples recorded in Patent No. )20,971 have been incorporated into this disclosure by ierence thereto, it is believed that this invention can understood to have general applicability to all serniystalline materials. I claim: 1. A method for producing a composite semicrystalline dy made up of individual preformed elements, a semiystalline body being made by the controlled crystallizan by heat treatment of a glass body, which comprises vplying to selected areas of at least one preformed eleent a coating of a cementing composition consisting esntially of at least one fluoride salt selected from the oup consisting of LiF, NaF, KP, MgF CaF SrF 1P PbF and ZnF placing the thus coated surface contacting relationship with another preformed ele- References Cited UNITED STATES PATENTS 2,399,770 5/1946 Taylor 65-43 2,687,364- 8/1954 Buerger et al l56--245 2,767,336 10/1956 Arenberg 31043.3 2,889,952 6/1959 Claypoole 65- 33 2,920,971 1/1960 Stool-(6y 65-33 3,137,602 6/1964 Lincoln 6536 X 3,189,512 6/1965 Stong 161192 DONALL H. SYLVESTER, Primary Examiner.

F. W. MIGA, Assistant Examiner. 

1. A METHOD FOR PRODUCING A COMPOSITE SEMICRYSTALLINE BODY MADE UP OF INDIVIDUAL PREFORMED ELEMENTS, A SEMICRYSTALLINE BODY BEING MADE BY THE CONTROLLED CRYSTALLIZATION BY HEAT TREATMENT OF A GLASS BODY, WHICH COMPRISES APPLYING TO SELECTED AREA OF AT LEAST ONE PREFORMED ELEMENT A COATING OF A CEMENTING COMPOSITION CONSISTING ESSENTIALLY OF AT LEAST ONE FLUORIDE SALAT SELECTED FROM THE GROUP CONSISTING OF LIF, NAF, KF, MGK2, CAF2, SRF2, BAF2, PBF2 AND ZNF2, PLACING THE THUS COATED SURFACE IN CONTACTING RELATIONSHIP WITH ANOTHER PREFORMED ELEMENT, AND THEREAFTER HEATING THE CONTACING ELEMENTS TO A TEMPERATURE OF AT LEAST 800*C. BUT BELOW THE DEFORMATION TEMPERATURE OF SAID ELEMENTS TO JOIN TOGETHER SAID ELEMENTS. 